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IEEE Transactions on Applied Superconductivity

Detection of the Josephson self-radiation from YBCO step-edge junctions in millimeter-wave

K. Lee, Ienari Iguchi

Published Jun 1, 1995• 2 citations
Publisher

Abstract

We have investigated both DC and AC Josephson effects of the YBa/sub 2/Cu/sub 3/O/sub y/ (YBCO) thin film step-edge junctions; single step-edge junction on LaAlO/sub 3/ substrate with the step angle about 50-60/spl deg/ and biepitaxial double step-edge junction made on MgO substrate with a CeO/sub 2/ seed layer. The Josephson self-radiation was directly detected using the total power radiometer receiver systems with receiving frequencies of K band (21-23 GHz) and millimeter-wave (46-48 GHz and 71-73 GHz) range, respectively. For single step-edge junctions, the Josephson self-radiation peaks exhibited at the voltages corresponding to the basic Josephson voltage-frequency relation. The maximum first-harmonic self-radiation power at receiving frequency f/sub REC/=72 GHz and Josephson linewidth were P(I)=2.0/spl times/10/sup -3/W and /spl Delta/f=3.62 GHz at 4.2 K, respectively. For microwave irradiation, the harmonic Shapiro steps and additional half integer steps with their quasi-periodic variation satisfying the Josephson equation V=(n/m)(hf/2e) were clearly observed. For double step-edge junctions, we also observed the steps corresponding to the two junction boundaries on the two steep steps. These behaviors described with different current-phase relations corresponding to the crystal orientation relationship between the two junction boundaries.>

DOI
10.1109/77.403171

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We have investigated both DC and AC Josephson effects of the YBa/sub 2/Cu/sub 3/O/sub y/ (YBCO) thin film step-edge junctions; single step-edge junction on LaAlO/sub 3/ substrate with the step angle about 50-60/spl deg/ and biepitaxial double step-edge junction made on MgO substrate with a CeO/sub 2/ seed layer. The Josephson self-radiation was directly detected using the total power radiometer receiver systems with receiving frequencies of K band (21-23 GHz) and millimeter-wave (46-48 GHz and 71-73 GHz) range, respectively. For single step-edge junctions, the Josephson self-radiation peaks exhibited at the voltages corresponding to the basic Josephson voltage-frequency relation. The maximum first-harmonic self-radiation power at receiving frequency f/sub REC/=72 GHz and Josephson linewidth were P(I)=2.0/spl times/10/sup -3/W and /spl Delta/f=3.62 GHz at 4.2 K, respectively. For microwave irradiation, the harmonic Shapiro steps and additional half integer steps with their quasi-periodic variation satisfying the Josephson equation V=(n/m)(hf/2e) were clearly observed. For double step-edge junctions, we also observed the steps corresponding to the two junction boundaries on the two steep steps. These behaviors described with different current-phase relations corresponding to the crystal orientation relationship between the two junction boundaries.>
We have fabricated YBCO step-edge Josephson junctions and measured the responses to millimeter and submillimeter irradiation. In the substrate milling process for the purpose of fabricating the step, the step angle was controlled using a Nb metal mask. At a step angle of 20 degrees, we obtained Josephson junctions, the characteristics of which are consistent with the RSJ model. We estimated the capacitance to be 4.4 fF using the RSJ model, but such a value for an 8 /spl mu/m wide and 300 nm thick junction seems too small. When the junctions were irradiated by 300 GHz radiation, Shapiro steps up to the 4th were observed. The junctions were used as mixers in the 100 GHz band, and as harmonic mixers in the 100 GHz LO and 700 GHz RF bands. Beat signals were observed in both cases. We also estimated the quasi-optical conversion losses of the step-edge junctions as mixers.>
We have investigated the Josephson radiation from different types of YBa 2 Cu 3 O 7 (YBCO) thin-film Josephson junctions: step-edge junctions (SEJs), biepitaxial junctions and SNS junctions with N=Au. The radiation was detected using a non-resonant radiometer system with a receiving frequency of 11-12 GHz. The current-voltage characteristics were measured simultaneously with the radiation spectra in the temperature range 4.2-90 K. All junctions exhibited a large emission peak at a voltage which was related to the frequency through the second Josephson relation. Typically, for high temperatures, and therefore small critical currents, the measured radiation linewidth agreed well with the theoretical predictions. At lower temperatures the experimental linewidths deviated from the theoretical values due to additional noise sources in the junctions. Some of the SEJs showed a non-monotonic dependence of the linewidth on temperature. It is suggested that such SEJ data may be discussed in terms of a model which treats the SEJ as an interferometer consisting of a parallel array of random Josephson junctions.
We have investigated the Josephson radiation from different types of YBa2Cu3O7 (YBCO) thin film junctions: step-edge (SEJ), biepitaxial, and superconductor-normal conductor- superconductor (SNS) with N=Au and PrBa2Cu3O7. The radiation was detected using a nonresonant radiometer system with a receiving frequency of 11-12 GHz. The current-voltage characteristics were measured simultaneously with the radiation spectra in the temperature range from 4.2 to 90 K. All junctions exhibited a large emission peak at a voltage which was related to the frequency through the second Josephson relation. Typically, for high temperatures, and, therefore, small critical currents, the experimental data of the radiation linewidth agreed well with the theoretical predictions of the RSJ model. At lower temperatures the experimental linewidths deviated from the theoretical values due to additional noise sources in the junctions. Some of the SEJs showed a nonmonotonic dependence of the linewidth on temperature. Such SEJ data will be discussed in terms of a model which treats the SEJ as an interferometer consisting of a parallel array of Josephson junctions.
Superconducting step-edge junctions were fabricated on step-edges in (100) LaAlO/sub 3/ substrates by sputter-deposited epitaxial YBaCuO and TlBaCaCuO thin films. The substrate steps were patterned by ion beam etching using metal film as a mask. The transport properties of the junctions were characterized by four-probe electrical measurements. The critical current-normal resistance product (I/sub c/R/sub N/) was larger than 0.2 mV (77 K) for most of the junctions. Clear Shapiro steps were observed in the current-voltage characteristics of the junctions with 36 GHz or 95 GHz millimeter-wave irradiation. The high frequency properties of these high T/sub c/ Josephson junctions showed that they were quite suitable for the Josephson harmonic mixer used in the digital phase locked millimeter and sub-millimeter wave sources.>
We have investigated the mutual phase interaction between a single detector junction and a phase-locked three-junction array of high-T/sub c/ Josephson junctions. The YBCO Josephson junctions were fabricated on a MgO bicrystal substrate. In the array junction structure, the dc bias current was fed to the junction array having parallel geometry with each pair of junctions shunted by a superconducting coplanar microstrip superconducting loop. The configuration of bias leads was a series connection of interlocking dc SQUIDs geometry which enables all junctions to oscillate at the same frequency. We measured the radiation power of a Josephson-junction array using an off-chip coupled to a radiometer and on-chip coupled to a single junction from centimeter- to millimeter-wave ranges. Clear self-induced Shapiro steps were observed in the current-voltage curves of the detector junction. The power transfered to the single detector junction was estimated from the modulation of Shapiro step height. The maximum detected power level was about 7 nW at frequency 150-250 GHz. The Josephson oscillation power excited the resonant mode coupled to the coplanar microstrip loops.
We report the strong microwave Josephson radiation from an array of high-T/sub c/ junctions on a MgO bicrystal substrate from centimeter- to millimeter-wave ranges. The dc bias current was fed to the junction array having parallel geometry with the pair of junctions shunted by superconducting loops. The configuration of bias leads was a series of interlocking dc SQUID's geometry which guaranteed the oscillation of all junctions at the same frequency. The phase differences between adjacent junctions with different I/sub c/R/sub n/ products could be controlled by an external small magnetic field. For a five-junctions array, we observed the coherent output power of about 13 pW without external magnetic flux, which was nearly five times higher than that of a single bicrystal junction. We observed the Josephson linewidth of the self-radiation in the coherent state to be less than 1 GHz by adjustment of the external flux.